Commercially available equipment for storing, transmitting and printing or displaying alphanumeric characters or other symbols has been developed which uses standardized code groups of binary digital data to describe each character. These code groups can be used to store and process the data in computers, and these code groups can be transmitted sequentially over common carriers or private transmission systems for further processing or print out at remote locations. These same code groups may be decoded by printing and viewing devices which then print or display the appropriate character. The location of the characters in the field is determined by additional code groups received to describe spaces desired between characters and lines of characters.
Many such printers and viewers have been designed to print out or display the data in specific areas large enough to include one character. Some such devices are capable of printing non-character graphics within a character size area, and then, proceeding to an adjacent area, printing an additional portion of non-character graphic information in response to appropriate signal inputs. With appropriate interface and signal inputs, non-character graphics can thus be printed out over large areas by many presently used character printing devices, and in the aggregate can be made to produce facsimile reproduction. However, facsimile scanning methods and apparatus commonly in use do not produce appropriate signals to be used by devices designed for sequential character printing or viewing, because the usual practice in facsimile and video systems is to scan the document or field, line by line, in a raster which covers the complete field.
There are in use high speed alphanumeric data printers known as line printers. These units use multiple printing elements or a matrix which covers a full line of elements across the page, together with line buffers and controls needed to print one line at a time. An appropriate interface could be used to convert such units into a facsimile printer but the result would be a slow and expensive device.
In addition, normal facsimile scanning does not provide signals that can be easily coded to produce a reduction in the amount of data which has to be transmitted. In data reduction systems which do effect such reductions, the scanning device must produce data at a variable speed scanning rate across the page or travel at very high speeds and store a large amount of data in a memory system to keep pace with rapidly changing rate of data needed. Both of these alternatives are cumbersome and expensive.
Furthermore, facsimile scanning apparatus in common use require extensive amounts of memory and logic to accomplish any reduction in data transmitted where there are redundant patterns extending in a direction perpendicular to the scan. For example, to examine and code a document feature covering a sixteen element space perpendicular to the scan would require a memory capacity of approximately 13,600 bits, and the logic to examine and encode the codable parts within this area would be complex.
Thus, with equipment heretofore available, a user of alphanumeric printers and facsimile equipment has been required to use two separate systems, even though the equipment is not being fully utilized. It has often been impractical to transmit facsimile images over the extensive networks of leased and switched lines used for alphanumeric printing (or "teleprinting" as it is sometimes referred to). These lines are often limited to data rates of 110 to 300 bits per second; a capability at which a full page of facsimile at 110 bits per second would take 2 hours and 10 minutes.
Accordingly, it is in general the object of this invention to provide a facsimile transmitter capable of efficient data compression, which generates signals that are compatible with sequential alphanumeric printers.
It is a further object of this invention to provide an efficient facsimile data reduction system which uses sequential sub-scannings of small finite rectangular sections of the document whose image is to be transmitted, and a coding method which encodes both vertical and horizontal patterns of redundancy.
It is another object of this invention to provide a highly efficient facsimile data reduction system which is operative as a binary two level digital system, or as a binary multi-level digital system per se which may alternatively be an effective substitute for an analog system.
It is still another object of this invention to provide a single printing device which can print out alphanumeric images from standard alphanumeric data, as well as facsimile images from appropriate facsimile data in sequence as received from a single channel or different channels.
Yet another object of this invention is to provide an efficient facsimile data reduction system using sequential sub-scannings of small finite rectangular sections of the document whose image is to be transmitted, and a coding method which encodes the sub-scan of the facsimile as a recognizable alphanumeric character, and sends out standard alphanumeric codes, or as a data reduced facsimile by encoding the redundancy, or as uncoded facsimile data as scanned from sub-sections.
Still another object of this invention is to provide an efficient, lower cost, data-reduced facsimile system in which the high speed scanning required is limited to a small, finite rectangular, sub-section of the document, utilizing a small, low-cost reading device and indexing from section to section in slower steps with a low cost transport means.
Another object of this invention is to provide a facsimile transmitter which produces signals from sequential sub-scannings of small finite, rectangular sections of the document whose image is to be transmitted wherein the area of the sub-scanned matches the alphanumeric character area used by the receiving printer when printing alphanumeric data.